International Journal of Molecular Sciences Article Interleukin-1β Modulation of the Mechanobiology of Primary Human Pulmonary Fibroblasts: Potential Implications in Lung Repair Marta Gabasa 1, Marselina Arshakyan 1 , Alejandro Llorente 1, Lourdes Chuliá-Peris 2, Irina Pavelescu 1, Antoni Xaubet 3, Javier Pereda 2 and Jordi Alcaraz 1,4,5,* 1 Unit of Biophysics and Bioengineering, Department of Biomedicine, School of Medicine, Universitat de Barcelona, 08036 Barcelona, Spain; [email protected] (M.G.); [email protected] (M.A.); [email protected] (A.L.); [email protected] (I.P.) 2 Departament of Physiology, Faculty of Pharmacy, Universitat de València, 46100 València, Spain; [email protected] (L.C.-P.); [email protected] (J.P.) 3 Pneumology Service, Hospital Clínic, 08036 Barcelona, Spain; [email protected] 4 CIBER de Enfermedades Respiratorias (CIBERES), 28029 Madrid, Spain 5 Institute for Bioengineering of Catalonia (IBEC), The Barcelona Institute for Science and Technology (BIST), 08028 Barcelona, Spain * Correspondence: [email protected] Received: 8 October 2020; Accepted: 8 November 2020; Published: 10 November 2020 Abstract: Pro-inflammatory cytokines like interleukin-1β (IL-1β) are upregulated during early responses to tissue damage and are expected to transiently compromise the mechanical microenvironment. Fibroblasts are key regulators of tissue mechanics in the lungs and other organs. However, the effects of IL-1β on fibroblast mechanics and functions remain unclear. Here we treated human pulmonary fibroblasts from control donors with IL-1β and used Atomic Force Microscopy to unveil that IL-1β significantly reduces the stiffness of fibroblasts concomitantly with a downregulation of filamentous actin (F-actin) and alpha-smooth muscle (α-SMA). Likewise, COL1A1 mRNA was reduced, whereas that of collagenases MMP1 and MMP2 were upregulated, favoring a reduction of type-I collagen. These mechanobiology changes were functionally associated with reduced proliferation and enhanced migration upon IL-1β stimulation, which could facilitate lung repair by drawing fibroblasts to sites of tissue damage. Our observations reveal that IL-1β may reduce local tissue rigidity by acting both intracellularly and extracellularly through the downregulation of fibroblast contractility and type I collagen deposition, respectively. These IL-1β-dependent mechanical effects may enhance lung repair further by locally increasing pulmonary tissue compliance to preserve normal lung distension and function. Moreover, our results support that IL-1β provides innate anti-fibrotic protection that may be relevant during the early stages of lung repair. Keywords: IL-1β; pulmonary fibroblasts; repair; cell mechanics; collagen; MMPs 1. Introduction There is a growing awareness that each tissue has unique mechanical properties and that such properties are essential to support tissue-specific functions [1,2]. In the context of normal lung physiology, pulmonary tissue remains soft and elastic to accommodate the cyclic volume changes required for breathing [3,4]. This normal tissue elasticity is transiently compromised in response to local tissue damage to facilitate repair [5–8]. In contrast, failure to resolve injury and restore normal lung architecture and function occurs concomitantly with persistent alterations in pulmonary tissue elasticity in a variety of physiopathological conditions, eliciting either a marked stiffening (as in pulmonary fibrosis or lung Int. J. Mol. Sci. 2020, 21, 8417; doi:10.3390/ijms21228417 www.mdpi.com/journal/ijms Int. J. Mol. Sci. 2020, 21, 8417 2 of 16 cancer) or softening (as in emphysema) [3,9–11]. Accordingly, there is increasing interest in identifying key mechanistic aspects of the mechanobiology underlying normal tissue homeostasis and repair and how it becomes awry in disease conditions in the lung and other organs, with the ultimate goal to develop therapies that restore the normal tissue mechanical microenvironment and function [5]. The elasticity of lungs and other soft tissues is determined by the mechanical characteristics of cells and their surrounding extracellular matrix (ECM) as well as by the bidirectional cell-ECM mechanical interactions [3,4,12,13]. Following damage, tissue elasticity becomes temporarily disrupted as part of the normal tissue host response. Fibroblast rank among the stiffest pulmonary cell types [13–15] and have been identified as key regulators of tissue mechanics during repair as well as in cell-biomaterial responses owing to their unique ability to rapidly alter tissue contractility and efficiently remodel the ECM in response to reparatory cytokines [6,8,16]. Despite recent efforts towards dissecting the biological complexity underlying tissue repair in the lung and other organs [8,16], our overall understanding is still scarce. Moreover, from the mechanical standpoint, most previous studies on fibroblast have focused on their responses upon activation by transforming growth factor-beta (TGF-β), which becomes upregulated either transiently at the late stages of canonical tissue repair or chronically during fibrosis and cancer in the lung and other organs [8,17,18]. Indeed, we and others have consistently reported a marked fibroblast stiffening in response to TGF-β and have identified key underlying signaling events [15,19,20]. In contrast, little is known on the mechanobiology alterations of fibroblasts upon stimulation with inflammatory cytokines like interleukin-1β (IL-1β), as it occurs during earlier stages of tissue response to damage [6–8]. Following tissue injury, damaged cells first release inflammatory factors that draw an influx of immune cells like neutrophils and monocytes [16]. IL-1β is one of the most well-studied members of the important IL-1 family of proteins that are key regulators of inflammation and tissue homeostasis in the lung and other organs [21–23]. IL-1β is primarily expressed by monocytes and macrophages stimulated by pathogen products or factors released by damaged cells, whereas it is not generally expressed in healthy tissue cells [22,24]. The effects of IL-1β contribute to the regulation of local inflammatory and repair responses, and its dysregulation has been implicated in numerous lung physiopathological conditions, including pulmonary fibrosis, asbestosis, chronic obstructive pulmonary disease (COPD), emphysema, severe cases of COVID-19, and other types of acute lung injury [23–27], which have drawn the interest of the pharmaceutical industry [23]. However, while there is a clear consensus that TGF-β stiffens fibroblasts [17], such consensus is missing on the direct mechanical impact of IL-1β on fibroblasts or other stromal cells since the few studies available on this topic have reported conflicting results [19,22,28,29]. Likewise, it is unclear the impact of IL-1β on ECM deposition by fibroblasts, particularly on fibrillar collagens [24,30], which could further alter tissue mechanics. The simplest and most widely used physical parameter to characterize the mechanical properties of cells and other biological samples is Young’s elastic modulus (E), which quantifies sample resistance to deformation [13]. Atomic force microscopy (AFM) has been extensively used to measure E locally in cells at the nanometer-length scale. For this purpose, AFM uses a nanometer-sized tip at the end of a flexible cantilever (the force sensor) to gently apply compressive forces on the cell while monitoring its local deformation or indentation [13,31]. We and others have used AFM to probe the mechanics of fibroblasts and other cell types cultured in normal-like and disease-like conditions, including TGF-β stimulation [15,31–34]. In contrast, AFM has not yet been used to probe fibroblast mechanics in response to pro-inflammatory factors like IL-1β. The goal of this work was to examine the impact of the pro-inflammatory cytokine IL-1β on the mechanics of human pulmonary fibroblasts by AFM as well as their collagen deposition and to assess its potential effects in fibroblast-associated repair processes. Int. J. Mol. Sci. 2020, 21, 8417 3 of 16 Int. J. Mol. Sci. 2020, 21, x FOR PEER REVIEW 3 of 16 2. Results 2. Results 2.1. Primary Human Pulmonary Fibroblasts Exhibit a Marked Stiffness Reduction upon Stimulation with the Pro-Inflammatory2.1. Primary Human Cytokine Pulmonary IL-1β Fibroblasts Exhibit a Marked Stiffness Reduction upon Stimulation with the Pro-Inflammatory Cytokine IL-1β A major downstream signaling event elicited by the pro-inflammatory cytokine IL-1β is the overexpressionA major of downstream cyclooxygenase-2 signaling (COX-2) event [ 35elicited]. To analyzeby the thepro-inflammatory effects of IL-1β cytokineon the mechanobiology IL-1β is the of pulmonaryoverexpression fibroblasts, of cyclooxygenase-2 we benefited from(COX our-2) previous[35]. To work,analyze which the identifiedeffects of treating IL-1β fibroblastson the withmechanobiology 10 ng/mL IL-1 βoffor pulmonary either 24 fibroblasts, h or 72 h as we su ffibenefitedcient to from achieve our a previous robust activation work, which of either identified COX-2 or thetreating extended fibroblasts COX pathway,with 10 ng/mL respectively IL-1β for [35 either,36]. We24 h confirmed or 72 h as the sufficient suitability to achieve of the lattera robust IL-1 β timingactivation and dose of either by analyzing COX-2 or COX-2the extended expression COX bypathway, Western respectively blot in pulmonary [35,36]. We fibroblasts confirmed from the a suitability of the latter IL-1β timing and dose by analyzing COX-2 expression by Western blot in randomly selected patient from our cohort, which revealed a consistent time-dependent (Figure1A) pulmonary fibroblasts from a randomly selected patient from our cohort, which revealed a consistent and dose-dependent (Figure1B) increase in COX-2. Accordingly, we used 10 ng /mL IL-1β thereafter. time-dependent (Figure 1A) and dose-dependent (Figure 1B) increase in COX-2. Accordingly, we Such an increase in COX-2 elicited by IL-1β did not compromise the typical elongated spindle-like used 10 ng/mL IL-1β thereafter. Such an increase in COX-2 elicited by IL-1β did not compromise the morphologytypical elongated observed spindle-like in untreated morphology control conditions observed in (Figure untreated1C).